This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-079358, filed Mar. 19, 2001, the entire contents of which are incorporated herein by reference.
The present invention relates to a suspension for disc drive incorporated in an information processing apparatus, such as a personal computer.
A hard disc drive (HDD) for recording in and reading information from a rotating magnetic disc or magneto-optical disc includes a carriage that can turn around a shaft. The carriage is rotated around the shaft by means of a positioning motor. The carriage is provided with an arm (actuator arm), a suspension mounted on the distal end portion of the arm, a head portion including a slider mounted on the suspension, etc.
When the disc rotates, air that gets into the space between the slider and the surface of the disc causes the slider slightly to lift off the disc surface. This suspension comprises a baseplate fixed to a suspension mounting surface of the arm, a beam portion formed of a precision plate spring, a flexure fixed to the beam portion, etc.
With the advance of compaction of information recorded in the disc and speed-up of the disc drive operation, the disc drive of this type has been requiring a shorter seek time. In order to shorten the seek time, the rotation of the disc must be speeded up further. If the disc rotates at high speed, however, an air turbulence that is generated near the disc surface causes the suspension to flutter, thus arousing a serious problem.
In order to improve various properties that are required of suspensions, a suspension has been developed by the inventors hereof such that a baseplate and a beam portion are connected to each other by means of a hinge member that is formed of a thin spring member. For example, a suspension 1 shown in FIG. 1 comprises a baseplate 2, beam portion 3, hinge member 4, etc. The baseplate 2 is formed having a boss portion 7 that can be fixed to an actuator arm 6. The hinge member 4 is provided with connecting portions 4a with a length L1 between the baseplate 2 and the beam portion 3. The connecting portions 4a are bendable in the thickness direction of the hinge member 4. The beam portion 3 is fitted with a flexure 8, which is provided with a slider 9.
In a hard disc drive 10 shown in FIG. 2, each suspension 1 is mounted on the actuator arm 6. The actuator arm 6 is turned around a shaft (not shown) by means of a positioning motor (not shown). The slider 9 is opposed to a surface of a disc 11. In this specification, a distance h1 from the surface of the disc 11 to a baseplate mounting surface 6a of the actuator arm 6 is referred to as Z-height.
As shown in FIG. 3, a convex pivot portion 15 (dimple as it is called in the art) for supporting the slider 9 for rocking motion is formed on the distal end portion of the beam portion 3. The slider 9 on the flexure 8 is rockable around a distal end 15a of the pivot portion 15. Even if the suspension 1 flutters, the slider 9 never moves in the direction indicated by arrow F when the beam portion 3 swings around the distal end 15a of the pivot portion 15.
Owing to variation in the Z-height, however, the beam portion 3 may possibly swing around a spot (e.g., pivot center designated by R1 or R2 in FIG. 3) that is off the distal end 15a of the pivot portion 15. As the pivot portion 15 is displaced in the direction of arrow F, in this case, the slider 9 inevitably moves in the direction of arrow F, thereby causing a track miss.
As the rotation of the disc 11 is speeded up, according to the suspension 1 described above, it becomes more important to restrain fluttering. Essential factors to restrain fluttering include the thickness of the baseplate 2, a width W1 of the baseplate 2, a distance L2 (referred to as baseplate length herein) from a center C1 of the boss portion 7 to a front end 2a of the baseplate 2, etc., as well as the length L1 (referred to as hinge length herein) of the connecting portions 4a of the hinge member 4.
Fluttering is not a problem with a suspension of which a length L3 from the center C1 of the boss portion 7 to the pivot portion 15 is 11.0 mm, for example. Possibly, however, fluttering may interfere with the operation of a suspension that has the length L3 of 14.5 mm.
In some cases, fluttering can be effectively restrained by enhancing the torsion stiffness of the suspension 1. It may be supposed, therefore, that fluttering can be restrained by increasing the width W1 of the baseplate 2 from, e.g., 4 mm to 4.5 mm. According to a diligent study made by the inventors hereof, however, fluttering cannot be satisfactorily restrained by only increasing the width of the baseplate 2.
Accordingly, the object of the present invention is to provide a suspension capable of restraining generation of fluttering in a disc drive with a disc that rotates at high speed.
In order to achieve the above object, a suspension for disc drive according to the present invention comprises a baseplate having a boss portion, a beam portion with a flexure, and a hinge member fixed to the baseplate and the beam portion and including a connecting portion bendable in the thickness direction thereof between the baseplate and the beam portion, the thickness of the baseplate ranging from 0.175 mm to 0.25 mm, the width of the baseplate being greater than 4.0 mm and not greater than 5.0 mm, the length of the connecting portion of the hinge member ranging from 0.1 mm to 0.7 mm, and the baseplate length from the center of the boss portion to the front end of the baseplate ranging from 4.0 mm to 5.1 mm.
According to the suspension of this invention, generation of fluttering can be restrained even when the disc rotates at high speed, so that the disc rotation can be speeded up without hindrance. According to this invention, moreover, generation of fluttering can be restrained with a high-rotation disc in the suspension that has a length of 14.5 mm.
The following is a description of the reason why the dimensions according to present invention are restricted to aforementioned values.
In FIG. 4, A1 represents the relationship between the thickness of the baseplate and the sway frequency of the suspension. The sway frequency is a resonance frequency in the sway direction (direction indicated by arrow S in FIG. 1) of the suspension. In FIG. 4, A2 represents the relationship between the thickness of the baseplate and the torsion stiffness of the suspension. If the thickness of the baseplate is smaller than about 0.17 mm, the sway frequency and the torsion stiffness lower suddenly. If the thickness of the baseplate exceeds 0.25 mm, the baseplate is too heavy to be feasible for practical use. Preferably, therefore, the thickness of the baseplate ranges from 0.17 mm to 0.25 mm.
In FIG. 5, A3 represents the relationship between the hinge length L1 and the sway frequency. In FIG. 5, A4 represents the relationship between the hinge length L1 and the torsion stiffness. If the hinge length L1 exceeds 0.7 mm, as seen from FIG. 5, the torsion stiffness, as well as the sway frequency, lowers considerably. It is to be desired, therefore, that the hinge length should be 0.7 mm or shorter. The shorter the hinge length L1, the higher the sway frequency and the torsion stiffness are. If the hinge length L1 is shorter than 0.1 mm, however, the manufacture of the suspension, adjustment of its performance, etc. are difficult. Accordingly, 0.1 mm is the lower limit of the hinge length L1.
In manufacturing the disc drive, the Z-height inevitably varies owing to limited accuracy of assembly. If the Z-height is subject to variation, the beam portion 3 swings around the spot (e.g., pivot center designated by R1 or R2 in FIG. 3) that is off the distal end 15a of the pivot portion 15. The longer a distance D1 or D2 from the distal end 15a of the pivot portion 15 to the pivot center R1 or R2, the greater the movement of the slider 9 in the direction of arrow F is. Preferably, therefore, the sensitivity to the variation of the Z-height (increasing rate of the distance D1 or D2) should be smaller.
In FIG. 6, A5 and A6 individually represent results of examination of the degree to which the pivot center is displaced from the distal end 15a of the pivot portion 15 when the Z-height of the suspension is changed. The axis of abscissa of FIG. 6 represents the Z-height, and the unit (1 mil) of the axis of abscissa is equivalent to {fraction (1/1,000)} inch or 25.4 xcexcm. The axis of ordinate of FIG. 6 represents the displacement (displacement in the direction D1 or D2 of FIG. 2) of the pivot center for each mil for the Z-height. The gentler the respective gradients of the segments A5 and A6, the lower the Z-height sensitivity is, and the less easily fluttering is caused.
FIG. 7 shows results of examination of the way the Z-height sensitivity changes when the baseplate length L2 is changed. The axis of ordinate of FIG. 7 represents the movement of the pivot center for each mil for the Z-height.
If the baseplate length is 5.1 mm or shorter, as indicated by a segment A7 in FIG. 7, the movement of the pivot center gently increases at a substantially fixed rate. If the baseplate length exceeds 5.1 mm, however, the movement of the pivot center increases suddenly. Thus, the Z-height sensitivity is suddenly enhanced at an inflection point corresponding to 5.1 mm, and remarkable fluttering develops.
In order to ascertain the reason why the aforesaid inflection point develops, the inventors hereof made diligent studies using a measuring device such as a laser vibrometer. Thereupon, it was revealed that the inflection point develops probably because a vicinity of the hinge portion of the baseplate swings. It was also found that if the length of the baseplate is 5.1 mm or shorter, the whole baseplate functions substantially as a rigid body, so that the Z-height sensitivity can be reduced. For this reason, according to the invention, the baseplate length L2 is restricted within 5.1 mm.
In FIG. 7, A8 represents data on a suspension having a baseplate width W1 of 4.0 mm. The suspension with the baseplate width W1 of 4.0 mm is expected such that the pivot movement changes on high levels if the baseplate is shorter than 6.1 mm, as indicated by a segment A8xe2x80x2 in FIG. 7. Therefore, the baseplate width W1 must be made greater than 4.0 mm. If the baseplate width W1 exceeds 5 mm, however, the baseplate is too heavy to be feasible for practical use, so that the upper limit of the baseplate width W1 is adjusted to 5 mm.
In FIG. 8, A9 represents the relationship between the baseplate length and the resonance frequency for a first torsion mode. In FIG. 8, A10 represents the relationship between the baseplate length and the sway frequency. Preferably, in practice, the first torsion frequency should be 6 kHz or above. According to the invention, therefore, the baseplate length L2 is adjusted to 4.0 mm or longer.
In the case where the distance (suspension length L3) from the center of the boss portion to the pivot portion (dimple) is adjusted to, for example, 14.5 mm, the suspension of the present invention can be made less liable to flutter even with use of a disc that rotates at high speed if the baseplate thickness, baseplate width W1, hinge length L1, and baseplate length L2 are adjusted to 0.2 mm, 4.5 mm, 0.6 mm, and 5.04 mm, respectively. In consideration of fluctuant factors of manufacture, such as tolerance, however, the suspension length L3, baseplate width W1, hinge length L1, and baseplate length L2 may be adjusted to 14.5 mmxc2x10.5 mm, 4.5 mmxc2x10.2 mm, 0.6 mmxc2x10.1 mm, and 5.04 mmxc2x10.06 mm, respectively.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.